Is WD-40 good for sharpening knives?

WD-40 is not good for sharpening knives. It is not a proper sharpening lubricant, and it does not improve edge formation the way water or honing oil does on the correct stone. On water stones, WD-40 can contaminate the surface and interfere with normal use. On oil stones, it may loosen grime, but it still is not the best choice for routine sharpening because it leaves residue and can trap debris. WD-40 is a cleaner and water displacer, not a sharpening medium. If a stone requires liquid, use what the stone is designed for. Matching the lubricant to the stone matters much more than using a general-purpose spray.